Shop around on the forums and ebay for a cheap (RETAIL version-Black Discs) copy of Tiger 10.4. With Leopard coming out next week, there will be plenty of people (including me) selling their Tiger Discs for reasonable prices......don't bother waiting for Leopard as your machine does NOT meet the minimum specs as listed by apple (867mhz or faster)
Once you have Tiger, you can:
A) Boot your machine from the discs and use the utilities menu to reset the current passwords to your own, OR
B) Erase the old OS and install a new, fresh OS and set your own passwords from the beginning
either way, dont forget to run software update to get your OS current, up to 10.4.10.......
As for photo work, it will depend on what type of work you will be doing & what level of sophisticated manipulations you need. iLife includes iPhoto, which is a good app for certain tasks, but there are plenty of apps out there for various levels of photo work, some are free/shareware, others are full blown commercial/pro apps, like Photoshop etc
We would need details of your work reqirments to recommend an app.......
ps.....Tiger RETAIL discs are DVD's, so make sure you have a DVD drive for the installation........